The present invention is related to machines used in performing railway right-of-way maintenance, and specifically to an automatic apparatus for removing threaded rail fasteners such as lag screws from wooden rail ties.
Conventional railroad rails are secured to the ties by so-called cut spikes which are driven by vertically directed forces through tie plate apertures into the wooden railroad ties. However, it has been found that certain portions of track, such as those bearing high tonnage traffic, as well as curved track sections, wear out faster than others, and require more frequent replacement. A side effect of frequent rail replacement is that the spikes have a tendency to loosen in the ties, especially in high tonnage sections of track.
As a result of these conditions, maintenance directors of railroads have determined that alternate fastening technologies to cut spikes should be explored. One alternative is to use so-called hairpin spikes, which have depending prongs designed to spread apart within the tie. Although hairpin spikes are used in some high traffic portions of track, they are somewhat limited in their application, in that such spikes are more difficult to drive into and pull from the ties using automatic equipment.
Another type of fastener which is being considered is the rail lag screw, which is similar in dimension to a cut spike, with the major difference being that the lag screw is designed to be used with a rail clip, and is axially rotated into predrilled holes in the tie. As such the lag screw has a threaded shank and a polygonal, multi-faceted or TORX head for engagement by suitable driving tools.
Yet another type of alternate rail fastening system employs relatively permanent concrete ties having threaded studs embedded therein for securing the rails with clips. Upon placement of a rail on the concrete ties, nuts are threaded onto the studs to secure the rail and the tie plate. Designers of conventional automatic railway maintenance equipment have not provided an automatic rail fastener remover which may remove threaded lag screws as well as such nuts.
A conventional technique for working with rail lag screws employs a hand-held rotary impact wrench which engages the head of the spike and can either drive or remove the lag screw at the direction of the operator. However, a major drawback of this technique is that during placement, either two operators are required, e.g. one to place the screws and one to operate the impact wrench, or a single operator must perform both tasks at an appreciably slower pace. Either way, this technique is inefficient and labor intensive.
Designers of conventional automatic spike driving machines have traditionally focused on the problems of rapidly, accurately and quietly driving cut spikes into the ties with vertically directed pushing and/or percussive forces without bending individual spikes. One example of a cut spike driving machine employing such vertical forces is commonly-assigned U.S. Pat. No. 5,191,840.
An automatic fastener applicator for threaded rail fasteners is disclosed in commonly-assigned U.S. patent application No. 08/103,056, filed Aug. 6, 1993 now U.S. Pat. No. 5,398,616 WHICH is incorporated by reference herein. Although the U.S. Pat. No. 5,398,616 discloses a device for accurately installing threaded rail fasteners into the ties, there is no disclosure for addressing the unique considerations involved in removing such fasteners.
Among the design considerations encountered in removing threaded rail fasteners of this type are that the fastener must be grasped or supported in some way to withdraw or pull it from the tie as it is being unscrewed. In addition, consideration must be paid to maintain the engagement between the rotating socket which engages the head or faceted portion of the fastener, and the head of the fastener itself. Another design consideration is that lag screws or other threaded fasteners have been known to become stripped in their holes in the tie. In such cases, merely counter-rotating the fastener head will not accomplish its removal. Similarly, lag screws may become misaligned or driven off center in the insertion process, which causes additional difficulties in their removal.
Thus, there is a need for a machine which can automatically and reliably remove threaded rail fasteners such as lag screws, and which permits an operator to remove stripped or misaligned screws or other fasteners, such as nuts threaded on fixed studs.
Consequently, a first object of the present invention is to provide an improved device which can automatically remove threaded rail fasteners, such as lag screws and/or nuts without manual handling.
Another object of the present invention is to provide an improved rail fastener removing device which can remove lag screws and/or nuts by supporting or pulling the fastener as it is being unscrewed.
Still another object of the present invention is to provide an improved rail fastener removing device which features the capability of removing stripped or misaligned fasteners.
A still further object of the present invention is to provide an improved rail fastener removing device which automatically unscrews and fully removes the fastener from the corresponding hole in the tie.